When in the field, soldiers typically carry canteens filled with water. In the past, the canteen was a rigid container typically carried on a duty belt or a backpack harness. However, in recent years the canteen has evolved into a highly deformable bladder having a tube terminating with a bite valve the soldier bites to open, allowing him/her to draw water from the bladder. As water is drawn from the bladder, it collapses and occupies less space.
One problem with respect to such a bladder hydration system is that with all the gear a soldier must wear and carry on combat missions, particularly extended missions, the canteen may become hidden or covered, making it impossible to ascertain quantity of water in the bladder. In other situations, the soldier may be lying or sitting, or in some other position where the bladder is squeezed into an irregular shape, or may be squeezed into an irregular shape by gear the soldier is carrying. These situations make a conventional liquid measuring system, as found in a rigid container, completely unworkable as the bladder is not rigid, and there is no assurance that the bladder will always be in an “up” orientation when the soldier wishes to check his supply of water.
One possible solution is the “buddy system” in which everyone checks everyone else's canteen levels. However, there are times when buddies are not around, are busy, just forget, or don't get it right. Furthermore, there are a number of bladder-type canteens that do not provide any easy or immediate access to physical measurement, such as those embedded or integrated into a back pack.
One approach to measuring the canteen fluid level is proposed in U.S. Pat. No. 6,840,100, and also some of the cited references therein, which use capacitance to infer a quantity of water in a hydration bladder. However, such a system suffers inaccuracies because of variable dielectric loading of the bladder sensors due to close proximity of the soldier's body, which has a dielectric constant of around 80 or so as opposed to air, which has a dielectric constant of around 1. In addition, close proximity of equipment, much of which is fabricated of metal, to the capacitive sensors would also radically change capacitance in the area around such a bladder. In addition, the capacitance of the bladder will change when the bladder is squeezed into irregular shapes. The approach disclosed in U.S. Pat. No. 6,840,100 attempts to compensate for these problems through various means, but it is at least a very complicated scheme, and likely still highly susceptible to bias from the local effects of soldier's gear and local environment, both of which make it more expensive and less reliable than desired. From the foregoing, a capacitive system for a hydration bladder appears generally unworkable to accurately and reliably measure a quantity of fluid therein.
Another approach is using bend sensors that measure bending of the bladder. Such a system would require a number of bend sensors positioned throughout the bladder, and complex signal processing to integrate readings from each. Here, distension of the bladder may correlate with quantity of water in the bladder, with more water producing more curvature. If the soldier is standing, then bend sensors would measure low bending at the top of the bladder, and higher bending at lower regions of the bladder. However, if the bladder is squeezed into an irregular shape by surrounding gear, or some portion of gear is lying on or protruding into the bladder, then fullness readings will be inaccurate. Similar arguments hold for trying to use stress or tension sensors. In addition, such a system would be expensive to produce and complicated to the point of being unreliable under combat and field conditions.
Acoustic sensors are a possibility, but there is no data suggesting such a system will work. For instance, if one monitors sloshing sounds, such sounds would disappear if the soldier is still or resting. Where a sonar-type system is used, it would be simple for enemy forces to develop listening devices that could pinpoint position of troops from sound of such a system. Further, such a system would require significant signal processing, making the system expensive and prone to failure.
Conventional fluid flow sensors might be adapted for this application, as taught by Perkins in U.S. Pat. No. 6,212,959. However accurate flow sensors tend to be complicated and cost-prohibitive. Also they only measure the flow leaving the bag. Without a second flow sensor to monitor how much fluid is entering the bag, it is easy for a flow sensor to drift away from accurate fluid level measurement. A fluid flow sensor inherently fails to provide an accurate or reliable fluid-volume or fluid level measurement.
In one embodiment, a fluid level sensor optimized for military hydration systems must meet demanding specifications. It must tolerate wide variations in orientation, temperature, fluid composition, and pressure. It must be easy to operate, simple, reliable, low-cost, low-power, light-weight, low-maintenance, and accurate. Ideally, it must draw minimal amounts of power, or scavenge necessary energy from the environment so as not to require batteries. A fluid level sensor optimized for military hydration systems must reliably answer the question “how much water is left in your canteen?” in harsh military training and operational environments while meeting all these demanding specifications.
In view of the foregoing, there is a need for a volume and fluid level sensor and method optimized for military hydration systems. There is a further need for a volume and fluid level sensor and method that can yield reliable and accurate level measurements even in a flexible container at arbitrary orientations. Additionally, there is a need for a volume and fluid level sensor and method that allows easy determination of fluid level by an individual without the assistance of buddies or comrades. Finally, there is a need for a volume and fluid level sensor and method that can operate with minimal power, prolonging battery life, or dispensing with batteries all together and operating off of scavenged energy.
Accordingly, it is one object of the present invention to provide a volume and fluid level sensor and method optimized for military hydration systems. It is a further object of the present invention to provide a volume and fluid level sensor and method that can yield reliable and accurate level measurements even in a flexible container at arbitrary orientations. Yet another object of the present invention is to provide a volume and fluid level sensor and method that allows easy determination of fluid level by an individual without the assistance of buddies or comrades. A still further object of the invention is to provide a volume and fluid level sensor and method that can operate with minimal power, prolonging battery life, or dispensing with batteries all together and operating off of scavenged energy.
In addition to these objects, it is also an objective of this invention provide a volume and fluid level sensor to measure a defined, nominally enclosed volume, where the volume may contain either substance or void or a combination, with the purpose of sensing environmental changes that produce changes in the volume, or sensing mechanically induced changes to the volume such as from tactile impression.
In accordance with the foregoing, Applicants propose a system and apparatus for determining a volume or degree of inflation of a flexible bladder, which may be used to infer a quantity of fluid or gas or combination thereof in such a bladder. Applicants further propose a system and apparatus for determining the volume or degree of distention of a flexible solid, which may be used to infer a change in some environmental or other physics parameter, or the mechanical impress to the deformable solid by air pressure, a foreign body or tactile pressure. The system and apparatus is lightweight, simple in its fabrication and low in cost, and reliable in operation. In hydration systems, Applicants' system and apparatus is highly durable, consumes little electrical power, or possibly scavenges power from its surroundings, and is insensitive to changes in shape and close proximity of metal objects and other objects that would interfere with capacitive and magnetic systems. Similar benefits are enjoyed by other bladder volume or media quantity applications such as measuring intravenous bags. In physics and environmental parameter measurement applications, Applicant's system and apparatus enjoys similar advantages and offers new means for measuring such parameters. In mechanical and tactile impress applications Applicant's system and apparatus offer a new method for sensing mechanical and human contact and pressure that does not depend on more error prone and less reliable capacitive or mechanical switch methods
With these and other objects, advantages, and features of the invention that may become hereinafter apparent, the nature of the invention may be more clearly understood by reference to the detailed description of the invention, the appended claims and to the several drawings herein.